Project II focuses on cognitive variables that may be part of the extended phenotype present in first-degree relatives of individuals with autism. Specifically, this project will focus on the executive function abilities of family members of autistic probands. Initial cognitive studies of parents and siblings focused on general impairments (e.g., mental retardation, learning disabilities), providing mixed evidence for a cognitive endophenotype. More recent investigations focusing on specific cognitive impairments that may aggregate in the families of autistic probands have been more promising, however. Project II concentrates on the integrity of one specific set of neuropsychological processes, executive functions, in family members of autistic probands. To examine whether executive deficits are stratified as a function of proband intellectual level, performance of parents/siblings of non-retarded autistic individuals will be compared with parents/siblings of children with learning disabilities (matched on IQ to autistic probands), while parents/siblings of mentally retarded autistic children will be compared to parents/siblings of probands with Down Syndrome (again matched on IQ to autistic subjects).